That happens:- if you ping a broadcast address, because you send one ping and get many answers back.- if two or more systems have the same IP and both send an answer back.- if your NIC is in promiscious mode and you have a not so smart switch (or hub) which sends the ping also back to the pinging system.- if you bridging 2 vNICs/pNICs

Workaround:

If you connect 2 teaming pNICs in 2 different swithes (not smart enough).